1. Field of the Invention
The present invention relates to a bearing structure applicable to a rotary member, such as a roller-like member, as well as to a toner storage device and an image forming apparatus provided with the bearing structure.
2. Description of the Related Art
In image forming apparatuses using electrophotographic technology, such as copying machines and printers, photosensitive drums are wide used as image carrying members. Generally, image forming operation performed by using a photosensitive drum is as follows. A charging device uniformly charges a surface of the photosensitive drum to a specific electric potential and an exposure unit projects a light beam emitted from a light emitting diode (LED) onto the surface of the photosensitive drum. The electric potential of the surface of the photosensitive drum is attenuated in areas exposed to the light beam, whereby an electrostatic latent image of an original image is formed on the drum surface. A developing unit develops the electrostatic latent image, thereby forming a toner image on the surface of the photosensitive drum. The toner image is transferred to a sheet of paper when the sheet is passed through an image transfer area where the photosensitive drum is held in contact with or in close proximity with a transfer roller.
An image forming apparatus includes a number of rotary members which rotate about longitudinal axes thereof, such as a photosensitive drum, a development roller, a cleaning roller, a fixing roller, a toner transporting screw and a sheet transport roller. Performance of these members as rotating elements, or rotational performance thereof, exerts a direct influence on various performance capabilities of the apparatus, such as image forming capability, toner image fixing capability, toner transporting capability and sheet transporting capability. It is therefore important to smoothly rotate the rotary members. For this purpose, each of the rotary members is provided with bearing structures at ends of a rotary shaft thereof for supporting the rotary shaft to permit the rotary member to smoothly rotate about the longitudinal axis.
Japanese Unexamined Patent Publication No. 2008-39865 describes a waste toner collection container provided with an example of the aforementioned kind of bearing structure. This waste toner collection container contains a transporting screw and has a bearing structure which includes a through hole formed in the container so that a rotary shaft of the transporting screw is fitted in the through hole. Generally, the bearing structure includes such functional elements as ball bearings to provide satisfactory rotational performance. Nevertheless, bearing structures with simplified arrangements, such as those employing through holes like the one mentioned above or recesses formed in walls of a housing for fitting ends of rotary shafts for the sake of compact design and cost reduction without using the functional elements, are used quite often in practice.
There are cases where a lubricant like grease is used in the bearing structure to improve the rotational performance thereof. The use of the lubricant serves to smoothen sliding motion of the rotary shafts, enhance wear resistance thereof and prevent generation of unpleasant noise. For example, there is a case where a lubricant is injected into or applied to a recess formed in a wall of a housing which supports an end of a rotary shaft of a rotary member during a process of assembling an apparatus.
On the other hand, however, there is a possibility that the lubricant leaks from the recess in the wall which supports the end of the rotary shaft, resulting in a shortage of the lubricant. The shortage of the lubricant can worsen the sliding motion of the rotary shaft and cause generation of unpleasant noise. Additionally, leakage of the lubricant to undesired areas can potentially smear a curved outer surface of a roller-like member or a sheet of paper or contaminate a large quantity of toner collected from the surface of the photosensitive drum prior to development. Particularly if the lubricant leaks to an area where a large quantity of toner is present, the toner will gather into a mass or stick to that area, potentially causing such problems as an increase in torque required for rotating the rotary member or lockup of rotation thereof.